1. Field of the Disclosed and Claimed Inventive Concepts
The presently disclosed and claimed inventive concept(s) relates to an associative thickener composition used to control the solution viscosity and other rheological properties of associative thickeners in aqueous media. More particularly, the associative thickener composition comprises a water dispersible polymer modified with a first hydrophobic group and a low VOC organophosphate, and is used to control the viscosity of high solids solutions of nonionic synthetic associative thickeners.
2. Background and Applicable Aspects of the Presently Disclosed and Claimed Inventive Concept(s)
Associative thickeners (ATs) have become rheology modifiers of choice to control the rheology of various aqueous based systems. Notably, their use to control the rheology of water-borne coatings continues to grow. They can be added to control the viscosity of the coatings during their manufacture as well as during applications. They can particularly be used to achieve several desirable application properties including spatter control, sag resistance, and good flow and leveling. In addition, good film build and development of full gloss potential after the coatings dry are highly desirable to achieve good hiding and appearance of the dried film respectively. ATs are water-soluble polymers modified with a small amount of hydrophobic groups. They can associate among themselves through their grafted hydrophobes as well as with other hydrophobic components present in a water-borne coating formulation leading to the development of a three-dimensional network.
Currently, there are three classes of commercial ATs available in the market place. These are: (a) hydrophobically modified hydroxyethylcelluloses (HM-HECs), (b) hydrophobically modified nonionic synthetic polymers, and (c) hydrophobically modified polyacrylates. In many water-borne systems, hydrophobically modified nonionic synthetic polymers are preferred over HM-HECs or hydrophobically modified polyacrylates as they can provide several desirable properties not offered by the latter.
In the last three decades, hydrophobically modified nonionic synthetic polymers have gained significant commercial importance. They are colloquially referred to in the market place as nonionic synthetic associative thickeners (NSATs).
Rapid incorporation of NSATs in the solid form into water-borne systems is very difficult. Currently NSATs are sold in the liquid form by dissolving the polymer in water containing 10-40% of the polymer. Since certain NSATs build up significant viscosity (>1000 cps) even at >2 wt % concentrations, the delivery of high-solids (>2 wt %) solutions of NSATs which are easily pourable, drainable under gravity or pumpable is challenging. To mitigate this problem, additives can be used to lower the solution viscosity of high-solids (>10 wt %) solutions of NSATs. Since they suppress the solution viscosity of NSATs, they are often referred to as “viscosity suppressants”.
While organic solvents (e.g., butyl Carbitol®, ethylene glycol and propylene glycol) and co-solvents can effectively suppress the solution viscosity of NSATs, their use has been recently discouraged as they are volatile. During the manufacture of coatings as well as during the drying of coatings, the volatile organic compounds (VOCs) present in coatings are released to the environment. Consequently, they pose a potentially serious environmental hazard and human health risks during the manufacture as well as after they are applied. They can also negatively impact the rheological performance of NSATs in an intended application. Due to enforcements of strict governmental regulations to control the emission of VOCs, the coatings industry is under pressure to comply with government regulations on VOCs. Their goal is to eliminate or significantly lower the amounts of VOCs in coatings and comply with local regulations. Therefore, there is drive to do away with VOCs in raw materials and formulations ingredients used to formulate water-borne coatings.
To suppress solution viscosity of NSATs, another approach is described in U.S. Pat. Nos. 5,137,571 and 5,376,709 that disclose the use of cyclodextrins or their derivatives to suppress the solution viscosity of hydrophobically modified ethoxylated polyurethanes, hydrophobically modified alkali-soluble emulsions, hydrophobically modified hydroxyethylcellulose, or hydrophobically modified polyacrylamides. The use of cyclodextrins to suppress the solution viscosity of hydrophobically modified poly(acetal-polyethers) and other non-urethane NSATs is described in U.S. Pat. No. 6,809,132 and U.S. Pat. No. 6,900,255 respectively. While cyclodextrins are non-volatile, they are expensive and may not efficaciously suppress the solution viscosity of NSATs bearing certain types of “complex” hydrophobes.
U.S. Pat. Nos. 5,916,935 and 6,057,398 describe the preparation of a concentrated solution of thickeners by forming an admixture of a non-urethane associative thickener compound and surfactants in conjunction with water and an organic solvent and subsequently azeotropically distilling off the organic solvent. The associative thickener solution thus obtained is typically essentially free of VOCs.
The use of surfactants to suppress the solution viscosity of NSATs is described in U.S. Pat. Nos. 5,425,806, 6,020,407 and U.S. Pat. No. 6,150,445. However, if a nonionic surfactant used for viscosity suppression of NSATs has low molecular weight it can contribute to VOC. Examples of such surfactants can include, but are not limited to, ethylene oxide adducts of low carbon chain fatty alcohol (<C10 carbon alcohol) with fewer (<4) alkylene oxide units.
Since even low VOC levels present in raw materials used to formulate the coatings can have a significant contribution to the total VOCs of the final coatings formulation, coating formulators have a preference for raw materials with very low or no VOCs.
The use of an acid to suppress the solution viscosity of hydrophobically modified ethylene oxide urethane (HEUR) polymers bearing aminated hydrophobes is disclosed in U.S. Pat. No. 7,741,402. By treating the aqueous solutions of the aminated polymers with an acid, the nitrogen centers of the aminated hydrophobes are quaternized. In other words, a cationic polymer is formed in solution. Due to quaternization of the nitrogen centers of the aminated hydrophobes, they repel each other and cannot undergo inter-chain hydrophobic associations to build high solution viscosity under acidic environment. When the acidified polymer solutions of these polymers are added to an aqueous media with alkaline pH (pH>7), the quaternized nitrogen centers revert to a certain degree to the neutral amine form and occasion hydrophophobic association leading to enhanced solution viscosity. The degree of this reversal of the quaternary nitrogen centers to the amine form would depend upon the pH of the aqueous media where it is being used. The drawback of this system is that the high solid solutions of the aminated polymer cannot be delivered using acids.
In addition, quaternization of the nitrogen centers in the aminated polymers could promote interactions with anionic species present in the aqueous media leading to insolubilization or inefficient viscosification of the system. Because of these, the use of aminated polymers delivered using an acid is somewhat restricted.
There is a need to design alternative viscosity suppressants that would efficiently lower the solution viscosity of NSATs and yet would be devoid of the deficiencies of currently used viscosity suppressants, viz., nonionic organic surfactants, cyclodextrins and acids.